Abstract
Astrocytes synthesize and release endozepines, a family of regulatory peptides, including the octadecaneuropeptide (ODN) an endogenous ligand of both central-type benzodiazepine (CBR) and metabotropic receptors. We have recently shown that ODN exerts a protective effect against hydrogen peroxide (H(2)O(2))-induced oxidative stress in astrocytes. The purpose of the present study was to determine the type of receptor and the transduction pathways involved in the protective effect of ODN in cultured rat astrocytes. We have first observed a protective activity of ODN at very low concentrations that was abrogated by the metabotropic ODN receptor antagonist cyclo(1-8)[DLeu(5)]OP, but not by the CBR antagonist flumazenil. We have also found that the metabotropic ODN receptor is positively coupled to adenylyl cyclase in astrocytes and that the glioprotective action of ODN upon H(2)O(2)-induced astrocyte death is PKA- and MEK-dependent, but PLC/PKC-independent. Downstream of PKA, ODN induced ERK phosphorylation, which in turn activated the expression of the anti-apoptotic gene Bcl-2 and blocked the stimulation by H(2)O(2) of the pro-apoptotic gene Bax. The effect of ODN on the Bax/Bcl-2 balance contributed to abolish the deleterious action of H(2)O(2) on mitochondrial membrane integrity and caspase-3 activation. Finally, the inhibitory effect of ODN on caspase-3 activity was shown to be PKA and MEK-dependent. In conclusion, the present results demonstrate that the potent glioprotective action of ODN against oxidative stress involves the metabotropic ODN receptor coupled to the PKA/ERK-kinase pathway to inhibit caspase-3 activation.
Publication types
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Research Support, Non-U.S. Gov't
MeSH terms
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Adenylyl Cyclases / metabolism
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Animals
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Apoptosis / drug effects*
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Astrocytes / cytology*
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Astrocytes / drug effects*
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Astrocytes / enzymology
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Astrocytes / metabolism
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Cyclic AMP-Dependent Protein Kinases / metabolism*
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Diazepam Binding Inhibitor / pharmacology*
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Extracellular Signal-Regulated MAP Kinases / metabolism
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Glutathione / metabolism
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Hydrogen Peroxide / pharmacology*
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MAP Kinase Signaling System / drug effects
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Mitochondria / drug effects
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Mitochondria / metabolism
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Mitogen-Activated Protein Kinases / metabolism*
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Neuropeptides / pharmacology*
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Neuroprotective Agents / pharmacology
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Oxidative Stress / drug effects
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Peptide Fragments / pharmacology*
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Phosphorylation / drug effects
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Rats
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Rats, Wistar
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Receptors, Metabotropic Glutamate / metabolism
Substances
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Diazepam Binding Inhibitor
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Neuropeptides
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Neuroprotective Agents
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Peptide Fragments
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Receptors, Metabotropic Glutamate
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diazepam binding inhibitor (33-50)
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Hydrogen Peroxide
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Cyclic AMP-Dependent Protein Kinases
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Extracellular Signal-Regulated MAP Kinases
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Mitogen-Activated Protein Kinases
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Adenylyl Cyclases
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Glutathione
Grants and funding
The authors wish to thank Mr Samir Elbahi for skillful technical assistance. Y.H. and K.H. were recipients of fellowships from the University of Tunis El Manar and a France-Tunisia exchange program CMCU-Utique. B.S. and S.D. were recipients of fellowships from the University of Tunis El Manar and a France-Tunisia exchange program Inserm-DGRS. This study was supported by the Research Unit UR/11ES09, an Inserm-DGRS program (to M.A. and M.C.T.; grant number M 10/M), Inserm (U982), the Institute for Medical Research and Innovation (IRIB), the Région Haute-Normandie and a France-Tunisia exchange program CMCU-Utique (grant number 07G0822). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.